For shortening an umbrella length and volume when folded for convenient carrying or storage purpose, the ribs of the rib assembly can be made as multiple folds and the central shaft be made as consisting of plural tubes which may be telescopically engageable with one another.
When the umbrella is opened, a spring catch should be provided in the central shaft for locking a runner of the ribs on the spring catch, which is depressed into the central shaft when retracting the tubes and closing the umbrella. The top tube of the telescopic central shaft should have a minimal diameter or width for a multiple-fold umbrella such as a four-fold or five-fold umbrella, thereby causing a great difficulty to install the spring catch in such a small top tube of the central shaft.
U.S. Pat. No. 4,739,783 disclosed a shortening link means of multiple-fold umbrella including a rib assembly having a third link (3) slidably engageable with a fourth link (4). The link (3) is slidably held in link (4) to thereby weaken the strength and stability of the rib assembly. Meanwhile, when opening or closing the umbrella, the extending or retraction of the ribs are initiated merely by the first link (1) and second link (2), without the aids of the third link (3) since the outer end (32) of the third link (3) is free moved in the fourth link (4) having no linkage connection therebetween. So, the rib assembly of such a conventional multiple umbrella can not be opened or closed very smoothly.
The present inventor has found the drawbacks of the conventional umbrella and invented the present multiple-fold umbrella.